Cauliflower (Brassica oleracea Var. botrytis) is a crop of the Cruciferae/Brassicaceae, or Mustard, family that also includes crop plants such as broccoli, cabbage, kale, turnips and mustard. Cauliflower plants for commercial production are typically started in a greenhouse from seeds. After about 35 to 40 days cauliflower seedlings are transplanted to the field, where they are grown for another 40-300 days, depending on variety and local growing conditions, to maturity and harvest. During the curd initiation phase the meristem of the cauliflower plant forms a generative bud; this bud will develop into the mature flower head, or curd, which is the harvested and marketed part of the plant.
Whiteness of the curd is a desirable trait in cauliflower. Curds of conventional cauliflower varieties turn from creamy white to yellow when exposed to light, particularly the natural sunlight of field production. Creamy white curds that have yellow patches or are totally yellow are undesirable and declassify the product. Maintenance of the whitest possible curd in cauliflower is achieved by a combination of variety selection and the cultural practice of covering or tying leaves together over the curds. These cultural practices are labor intensive, and expensive. Covering is initiated at about the point that the curd reaches a few inches in diameter. Workers are required to enter the fields at this bud stage, and manually fold the large outer leaves of the plant over the head of the cauliflower to prevent the sun exposure during curd development. It is typically about one week from tying to harvest. The plants must be examined during this period to see that the tying is secure, as even small amounts of sunlight coming through cracks in the leaves can result in discolored patches on the curd. Examination of the plants is also needed to assess when the curd is ready to be cut and harvested. Overmature curds also develop other undesirable traits. For instance it may become loose and ricey, at which stage the quality of the cauliflower is lost.
Plant breeding has been used to develop several varieties of cauliflower that display a curd with enhanced whiteness. Even in these varieties, however, exposure to the sun will discolor the curd, affecting the commercial value of the crop.
In recent years, breeders have also evaluated the “persistent white” trait in cauliflower, i.e., a curd that will not discolor from white to creamy when exposed to sunlight. Descriptions of this trait can be found, for example, in Dickson, et al, Persistent White Curd and Other Curd Characters of Cauliflower (1980) Amer. Soc. Hor. Sci 105(4):533-535; and Dickson, M. H., Male Sterile Persistent white Curd Cauliflower NY 7642A and its Maintainer NY 7642B (October 1985) HortScience, Vol. 20(5), 957. These authors describe the development of male sterile persistent white curd cauliflower NY 7642A and its maintainer NY7642B, though certain unfavorable traits were linked to a persistent white character, namely, riciness, bracting and low curd density. Persistent white varieties have continued to have problems with these quality traits, making them poor candidates for commercial production.
Thus, there is a need for improved cauliflower varieties having a white quality trait but lacking the unfavorable traits present in previous persistent white varieties.